My 9 year old step daughter has had the lower and upper removable for about a month. Somehow, the lower one flew out of her mouth when she was running in the yard. Apparently they weren't tight enough and she was playing with it with her tongue. I searched on my hands and knees for 3 days in the rain and even borrowed a metal detector trying to find it.....no such luck. $350 for a new bottom. Please make sure the patient is responsible enough for this pricey piece of equipment.....They need to be removed for snacks and gum...my step daughter is obsessed (addicted?) to both of these....and she really has no concept of things being expensive.